1. Field of the Invention
The invention relates to a pointing device, and more particularly to a three dimensional pointing device.
2. Description of the Related Art
FIG. 1 illustrates a conventional three dimensional (3D) pointing device 1, such as a 3D mouse, that includes a three-axis accelerometer 11 three-axis magnetometer 12, an angle calculating unit 13, a low-pass filter 14, and a two-axis coordinate converting unit 15. The three-axis accelerometer 11 measures an acceleration value on an X-axis, a Y-axis and a Z-axis of the conventional 3D pointing device 1. During motion of the conventional 3D pointing device, the three-axis magnetometer 12 measures a terrestrial magnetism value on the X-axis, the Y-axis and the Z-axis of the conventional 3D pointing device. The angle calculating unit 13 uses the acceleration value measured in the three-axis accelerometer 11 to calculate a roll angle and a pitch angle of the conventional 3D pointing device 1. Further, the angle calculating unit 13 uses the roll angle, the pitch angle, and the terrestrial magnetism value measured in the three-axis magnetometer 12 to calculate a yaw angle of the conventional 3D pointing device 1. The angle calculating unit 13 subtracts pre-stored initial yaw and pitch angles from the yaw and pitch angles calculated thereby to output an angular pointer signal corresponding to the motion of the conventional 3D pointing devices. The low-pass filter 14 filters out jitter noise, which results from human tremor, from the pointer signal to generate a filtered output. The two-axis coordinate converting unit 15 converts the filtered output from the low-pass filter 14 into an X-Y coordinate output that can serve as an input signal for a computer to control movement of a cursor on a screen of the computer display.
However, the low-pass filter 14 with a fixed bandwidth/gain may filter out the pointer signal corresponding to high-speed motion of the conventional 3D pointing device, thereby resulting in lack of precision. FIG. 2 illustrates an angular velocity (L1′) of the conventional 3D pointing device, and a processed angular velocity (L2′) obtained from the conventional 3D pointing device. It is noted that the conventional 3D pointing device has a relatively long latency time (TL). Therefore, the conventional 3D pointing device cannot instantaneously generate a pointing output in response to one operation.